Increased dietary cholesterol and saturated fat have been shown to be related to increased levels of plasma cholesterol (particularly in low density lipoproteins) and vascular disease. The purpose of this study is to determine the effects of dietary cholesterol, in combination with low or high intake of saturated fat, on human plasma cholesterol metabolism. The study will focus particularly on the biochemical reactions in plasma promoting the return of peripheral cell cholesterol to the liver (reverse cholesterol transport). Studies in human subjects and lower primates (babboons) have found such transport to be acutely stimulated in postprandial lipemia. Preliminary data now suggests that this stimulation is markedly inhibited by chronic (6-8 week) increased intake of dietary cholesterol. Young and older male volunteers will consume diets of traditional format differing in cholesterol and saturated fat content, prepared in the General Clinical Research Center. The plasma mass and activities of components of the reverse cholesterol transport pathway will be determined in fasting plasma, and during postprandial lipemia, in these subjects adapted to each diet. These measurements will include not only those made on the levels and compositions of the lipoproteins themselves, but also the enzyme and other catalysts promoting the modification and clearance of lipoprotein cholesterol. The data to be obtained will provide detailed new documentation of the effects of dietary cholesterol on plasma lipoprotein metabolism and in particular, indicate whether dietary cholesterol inhibits the return of peripheral cell cholesterol to the liver in human subjects.